PNEUMATIC METHOD FOR SEPARATING MINERAL RAW MATERIALS

Abstract

 The invention relates to the field of separating mineral raw materials and can be used for producing mobile separating plants which are intended for processing and classifying raw materials according to fractions virtually in any weather conditions, including at ambient air temperatures of -50 to +50°C. What is claimed is a pneumatic method for separating mineral raw materials, comprising placing raw materials which are to be separated on an air-permeable surface which traverses a separation chamber with a rising air flow that lifts light fractions from the air-permeable surface, the latter being in the form of a conveyor passing beneath the lower base of the separation chamber, in which, by selection of the velocity of the air flow, a dilute fluidized bed layer is formed from particles of a specified density, into which less dense particles enter and through which said particles pass without obstruction before being transferred with the rising air flow out of the separation chamber into a gravitational deposition chamber. What is novel is that the separation chamber is mounted at an inclination to the plane of the conveyor, wherein the lower base of said separation chamber is parallel to the plane of the conveyor, and the acute angle formed between the longitudinal walls of the separation chamber and the base thereof is oriented in the direction of movement of the conveyor.

Description

[0001] The invention relates to the field of separating mineral raw materials and can be used for producing mobile separating plants which are intended for processing and classifying raw materials according to their elements in any weather conditions, including at air temperatures of -50 to +50°C.

[0002] It is known, that one of the main methods for separating ores, coal, nonmetallic materials are specific density separation methods (i.e., gravitational methods). A reduction in quality of the raw materials that are extracted and increase in requirements of quality of concentrates which are supplied for further processing to power-engineering, metallurgic and chemical enterprises substantially increases requirements for the efficiency of raw-material separation methods to be used.

[0003] Similarly, it is known, that for the period of operation of separating plants and metallurgic processing plants, large amounts of mineral waste has been accumulated. Such waste not only contaminates the environment, but also occupy large land areas which are located in the direct vicinity to settlements, towns and other residential areas. Mostly, those mineral wastes are important raw materials for secondary processing. Thus, for example, byproduct from ferrochrome production contains 2 to 12% of metallic ferrochrome; whereas, inclusion of chrome in ore used in melting process constitutes 1 to 5%, such chrome is chemically-bound. Hence, secondary processing of the byproduct is not only capable of improving environmental condition of the respective regions, but also economically viable, whereas, technology of processing of the specified wastes must comply with a number of strict requirements.

[0004] Firstly, a raw-material separation technology must be universal, easily adjustable for processing of various kinds of mineral raw materials; at the same time, it must be suitable for separation of materials varying in density (e.g., coal, ore, technogenic wastes and nonmetallic raw materials). Processing procedure must provide a possibility to quickly and easily alter process modes depending on properties of raw materials to be processed, requirements as to quality of products of processing, etc., which will enable making module-type mobile separating plants having a low level of capital expenditures for their delivery and installation.

[0005] Secondly, the raw-material separation technology must be highly efficient, providing for high quality of the products obtained, as well so that after its application the byproducts that remain are unsuitable for further processing or industrial application.

[0006] Thirdly, the raw-material separation technology must be all-weather and year-round, so that the process is not season-related with temporary involvement of labor resources, but is uninterrupted with year-round employment of local population. Due to the foregoing reasons, the process cycle for raw-material separation must include ambient air temperature range -50 to +50 °C and must allow location of equipment in the open air or with the use of small shelters.

[0007] There is known a raw-material separation method which is widely used to-date; it is based on product separation by density in liquid medium (see. Razumov K.A. Perov V.A. "Designing of separating plants" M., Nedra 1982, pages 195-205, 268-282). In the availability of considerable and cheap water resources, the method allows to provide for sufficiently yielding raw-material separating process.

[0008] The main disadvantage of the known method of raw-material separating is impossibility of its application in winter conditions in open air conditions. In fact, construction of specialized plants operating on a round-year basis, requires substantial material and financial resources for ensuring heating. This does not allow to obtain competitive products using the well-known method under winter conditions even in middle latitudes with moderately cold winters (peak values of negative temperatures are within - 5 to -10 °C).

[0009] There is known another method of raw-material separating which is widely used to-date. It is based on product separation by specific density in air medium (see M.V. Verkhoturov "Gravitational separating methods" M., Max-Press 2006, pages 306-318), G.N. Shokhin A.G. Lopatin "Gravitational separating methods", M., Nedra1993., page 9), which includes supply of raw-material being separated into a gravitational deposition chamber. Said chamber makes reciprocating movements, it is equipped with a screen from the bottom of which airflow enters. During the motion process along the screen, heavy materials move downwards, while light materials move to the upper part of the layer being made of the product to be further processed.

[0010] This method allows to carry out a year-round raw-material separation in the open air or with the use of small shelters.

[0011] The principle disadvantage of the specified raw-material separating method is low efficiency of product separation process, high degree of presence of light materials in heavy products, so far as the process is carried out in the layer of the product placed on the screen. Increase in layer thickness which is necessary for generation of segregated layers of products of various densities, results in its high resistance and, as a consequence, in a low degree of its scrubbing and low efficiency of material separation. It is impossible to ensure quick conversion of manufacturing process for processing of different types of raw materials, so far as each separator is manufactured to process products with the preset density range.

[0012] Moreover, the specified method for raw-material separating does not allow to carry out highly efficient separation of raw materials by fractions due to high effect of raw-material humidity during the process.

[0013] The method which is the closest to the technical solution of the present invention is the method of pneumatic separating of mineral raw materials (see Eurasian patent No. 022959, Class B07B 4/08, BO3B 4/04, 2016), comprising placing raw materials, which are to be separated on an air-permeable surface which traverses a vertical (separation) chamber with a rising air flow that lifts light fractions from the air-permeable surface, the latter being in the form of a conveyor passing beneath the lower base of the vertical separation chamber, in which, by selection of the velocity of the air flow, a dilute fluidized bed layer is formed from particles of a specified density, into which less dense particles enter and through which said particles pass without obstruction before being transferred with the rising air flow out of the vertical separation chamber into a gravitational deposition chamber.

[0014] The method allows to carry out separating of raw materials in the open air or using light shelter on a year-round basis; as well, to perform quick re-adjustment of manufacturing process to process various types of mineral raw materials by the way of alternating air-flow speed.

[0015] The main disadvantage of the specified method is its insufficiently high performance of selection of particles of pre-set dimension, which is stipulated by the following reasons.

[0016] Firstly, when trying to increase performance of the method, it is necessary to proportionally increase the conveyor speed, which reduces the period of presence of particles of the pre-set dimension within the area of intake end (nozzle) of the vertical chamber and, in turn, this increases horizontal speed and horizontal component of kinetic energy of the particles moving on the conveyor.

[0017] Secondly, an increase in the conveyor speed automatically results in shifting and increase density of a dilute fluidized bed layer near the rear (along the conveyor movement) wall of the vertical chamber, which disturbs the general flow of particle motion (due to increasing the density of particles) in a pseudo-boiling layer, which prevents from passing particles of lower density through it, i.e. this results in removal of light particles with heavier particles and reduces separation process performance.

[0018] The basis of the invention is the aim to increase performance of the specified method along with preservation of separation process performance.

[0019] In a method of pneumatic separation of mineral raw materials, comprising placing raw materials which are to be separated on an air-permeable surface which traverses a separation chamber with a rising air flow that lifts light fractions from the air-permeable surface, the latter being in the form of a conveyor passing beneath the lower base of the separation chamber, in which, by selection of the rate of the air flow, the dilute fluidized bed layer is formed from particles of a specified density, into which less dense particles enter and through which said particles pass without obstruction before being transferred with the rising air flow out of the separation chamber into a gravitational deposition chamber, the specified aim has been achieved by the way that the separation chamber being inclined towards the conveyor plane, whereas its lower base is parallel towards the conveyor plane and the acute angle formed by longitudinal walls of the separation chamber and its base is directed towards the conveyor motion.

[0020] The specified location of the separation chamber and its base in relation to the conveyor surface, when increasing the conveyor speed allows to considerably reduce density of the fluidized bed layer near the rear (along the conveyor movement) wall of the separation chamber, due to more even distribution throughout the cross-sectional area of the separation chamber.

[0021] In order to increase the degree of extraction of particles with pre-determined density, the separation chamber is divided by internal longitudinal parallel partitions into two or more sequentially and/or parallelly positioned sections, whereas, lower ends of the sections are positioned in parallel to the conveyor plane, and upper ends of the sections are joined together inside the separation chamber by a single air flow which transfers particles to the gravitational deposition chamber. This is achieved due to the fact that in the separation chamber, which is designated for separating particles by the pre-determined gravity value, there is a multi-staged selection of the specified particles by way of simultaneous effect upon the specified particles by several sequential vertical flows each of which absorbs a specific particle in its designated section.

[0022] It is known that the separation chamber selects the particles with the density that is lower than the pre-set density, for example, 1.4 g/cm³. So far as the material being separated may contain a large number of particles with the density less than that of separation, dividing the separation chamber into the sections having equal or different cross sections in terms of area and, respectively, equal or differing speed of flows inside of them, will allow to perform staged separation of particles with the density less than that pre-determined density, thereby, reducing the load on the last chamber and increasing the efficiency of separation of particles with the density up to 1.4 g/cm³.

[0023] In order to perform multi-staged selection of particles with pre-set gravity, different sections of the separation chamber may have the same or different height of placement of ends of the sections above the conveyor, thereby, ensuring formation of the fluidized bed layer of equal or differing density in each section of the separation chamber, which will allow in first sections of the separation chamber to ensure pre-separation of particles with the density substantially lower than that pre-set, whereas, in last sections - to perform more accurate and efficient separation of particles by density.

[0024] Dividing the separation chamber into the sections located along the conveyor motion, allows to remove nonuniformity of the air velocity field in the separation chamber in the cross section (along the conveyor), and dividing the chamber into the sections located across the conveyor motion, allowing to liquidate nonuniformity of the air velocity field in the separation chamber both in cross and longitudinal section (perpendicular to the conveyor), as well as to prevent cross and longitudinal crossflows of particles of the fluidized bed layer as well as to ensure its uniformity throughout the chamber section. This effect is achieved due to resistance to air flow in the channel being proportional to the square of flow speed and, respectively, the flow is hampered more in the channels wherein the speed originally was higher and meets the least resistance in the channels with the minimal speed and, thus, as a result the flow speed in all the channels approaches the average value throughout the separation chamber.

[0025] Thus, the separation chamber which is installed inclined towards the conveyor plane, whereas, the plane of its base is located in parallel to the conveyor plane, allows to substantially (double and more) increase performance of the disclosed method as compared to the prior art, at the same time preserving or even increasing selectivity of the pneumatic method for mineral raw-material separation, which has no analogues among known methods to be currently applied with installations of pneumatic separation and thus, it meets the criterion of "inventive step".

[0026] The disclosed herein method is illustrated by Figures 1-7.

Figure 1 shows a block diagram for the installation of mineral raw-material separating, wherein the separation chamber is position vertically, like in the prototype, and arrows show motion path of mineral raw-material particles to be separated, which are taken-in from the air-permeable conveyor as well as their interaction with the air flow and the fluidized bed layer particles. Also, the same Figure shows shifting of the layer towards the rear (along the conveyor 30 movement) wall of the separation chamber, wherein: 1 - the separation chamber walls; 2 - direction of movement of intake air flow in the separation chamber; 3 - the air permeable conveyor with particles of mineral raw-material being separated 4; 5 - lower base of the separation chamber; 6a-6f - directions of motion of particles of mineral raw-material being separated, 7 - the gravitational deposition chamber, connected with the separation chamber by an intake duct 8, as well as a system of air intake 9 from the gravitational deposition chamber; 10 - a lock gate hatch for removal of separated mineral raw material 11.

Figures 2a and 2b show view A, which shows distribution of particles in the fluidized bed layer at low and high speeds of the conveyor: during the conveyor's high speed operation the fluidized bed layer is shifted towards the rear (along the conveyor motion) wall of the separation chamber.

Figure 3 shows a portion of inlet of installation for pneumatic separating, wherein the separation chamber is inclined, and arrows show a movement path of mineral raw-material particles to be separated, which are taken-in from the air-permeable conveyor as well as their interaction with the air flow and the fluidized bed layer particles. Further, uniform distribution of the fluidized bed layer in the chamber is shown, wherein: 12a-12b - the separation chamber walls; 13 - direction of motion of intake air flow in the separation chamber; 14 - the air permeable conveyor with particles of mineral raw-material being separated 15; 16 - plane of lower base of the separation chamber; and 17a-17b - directions of motion of particles of mineral raw-material being separated inside the chamber.

Figure 4 shows a portion of inlet of the installation for pneumatic separation, wherein the separation chamber is positioned inclined and consists of three sequentially installed sections which are located along the conveyor, whereas, lower ends of the sections are placed at the same height with respect to the conveyor, wherein: 18 - the separation chamber walls; 19a - 19c - directions of motion of intake air flows in the separation chamber sections; 20a-20c - planes of lower ends of the sections of the separation chamber; 21 - the air permeable conveyor with particles of mineral raw-material being separated 22; 23-35 - directions of motion of particles of mineral raw-material being separated in the lower ends of the sections of the separation chamber and in the fluidized bed layer.

Figure 5 shows a portion of inlet of the installation for pneumatic separation, wherein the separation chamber is positioned inclined and consists of the three sequentially installed sections which are located along the conveyor, whereas, lower ends of the sections are placed at different height with respect to the conveyor, wherein: 36 - the separation chamber walls; 37a - 37c - directions of motion of intake air flows in the separation chamber sections; 38a-38c - planes of lower ends of the sections of the separation chamber, placed at different height with respect to the conveyor 39 with particles of mineral raw-material 40 being separated.

Figure 6 shows a portion of inlet of the installation for pneumatic separation, wherein the separation chamber is positioned inclined and is multi-sectional, and consists of the three sequentially installed sections which are located along the conveyor and the three consecutively located sections, which are placed across the conveyor, whereas, lower ends of all the sections are placed at equal height with respect to the conveyor, wherein: 41 - multi-sectional inclined separation chamber which consists of three lines of the sections 43' - 45', located along the motion direction of the air permeable conveyor 42 and three lines of the sections 43" - 43"", placed crosswise to its motion. Fig. 7 shows a distribution of particles of mineral raw-material being separated inside the sections 43" - 43"".

[0027] In order to understand the present method, firstly, the processes taking place in the separation vertical chamber, as shown in Figure 1, is considered. Particles 4 of raw-material being separated, move within the air permeable belt-type conveyor 3. The finest fractions of the particles are filtered through the conveyor 3 and are removed from the particle separation area (the process of filtering through the conveyor 3 and removal of spilled particles conditionally is not shown schematically). Further, particles 4, moving on the conveyor 3, get to the intake area of the separation vertical chamber, which is limited by walls 1, wherein particles 4 with the air flow 2 are sucked through its open bottom opening 5. Thus, in the area adjacent to the open base 5 of the separation vertical chamber, there occur vortex flows of moving particles 6a - 6f, which are formed by simultaneous impact upon particles 4 by horizontal powers, which relate to their movement on the belt-type conveyor 3, as well as by vertical lifting forces being created by air flow 2. The specified flows of moving parts 6a - 6f form the fluidized bed layer from particles of pre-set density, into which only particles of density less than that the pre-set density pass through unrestricted; then, they by an ascending air flow are carried over from the vertical chamber through the intake air-duct 8 to the gravitational deposition chamber 7, from which by the air-intake system 9 rarefaction necessary for the particles 4 intake is formed. After accumulating particles in the gravitational deposition chamber 7, the lock gate hatch 10 is opened and deposited particles are removed. Gravity of the particles out of which the fluidized bed layer is formed, is pre-set by the air flow speed 2. At low motion speeds of the belt-type conveyor 3, and consequently, low performance of the method, distribution of particles in the fluidized bed layer corresponds to Fig. 2a; and when the speed of the conveyor 3 increases, distribution of particles is carried out as shown in Fig. 2b, i.e. the fluidized bed layer is shifted towards the rear (along the conveyor motion) wall of the vertical chamber. Whereas, performance of separation process in the vertical chamber is reduced. This is explained by the fact that when particles 4 move, in the fluidized bed layer occurs a flow, which ensures a separation of particles by gravity, as well as parasitic flows. Thus, for example, a light particle being moved along path 6d may come into contact with a particle of high gravity moving along path 6e, and taking into account, in this regard, availability of horizontal speed of particle 6e and its higher density, there is a possibility that this particle will lug off the particle moving along path 6d and will remove it from the separation chamber.

[0028] Thus, at an increase of motion speed of the air permeable conveyor 3 - there will be observed reduction of performance of particle separation in the separation chamber. In this regard, the only method which allows to increase performance of pneumatic separation of mineral raw materials, is an increase in motion speed of the air permeable conveyor 3. In order to address the specified issue, it is suggested to position the separation chamber inclined, as shown at Fig. 3. Due to the fact that the area 16 of the bed being taken-in is more than the area 5 of the vertical separation chamber (Fig. 1), and wall 12a of the separation chamber is inclined towards the conveyor motion 14, whereas, motion of particles in the fluidized bed layer is formed by two flows: a rising flow - directed along the angled walls 12a and vertical flow - descending towards the angled wall 12b, which results in organized circulation of particles. Thus, the fluidized bed layer under impact of particle flow 17a is shifted towards the front (along the conveyor movement) wall 12b and, thereby, the fluidized bed layer is leveled with respect to the whole area of the plane of lower base 16 of the separation chamber.

[0029] In order to increase the degree of extraction of particles with the pre-set density, the separation chamber can be separated by longitudinal partitions into two or more consecutively placed sections (see Fig. 4), the bases 20a-20c are parallel to the conveyor plane and are at equal distance from it. The specified effect can be explained by the following example. It is supposed that in the active mode in section one of the separation chamber can achieve 90% efficiency, i.e. removal of light particles from the chamber constitutes 10%. Thus, it is possible to extract 90% of light particles in the first section, and in the second section - further 90% of those light particles which got into the second section, i.e. overall effectiveness of separation in the two sequential sections will amount to 99%, at separation performance in one section equal to 90%. This solution allows to achieve substantial increase in the conveyor motion speed and, respectively, performance of the present method.

[0030] An embodiment of the present method as shown in Fig. 5 is now considered, wherein a three-sectional chamber is used; which lower bases of the sections to be located at different height from the chamber's surface. The specified method allows to ensure distribution of the fluidized bed layer in the sections of the separation chamber in such a manner, so that in the first sections (towards the conveyor movement) of the conveyor, which have fluidized bed layer of lower density, there takes place extraction of great bulk of particles with the density that is considerably lower than the pre-set threshold density, thereby a load to the last section is reduced, wherein the final removal of particles with the density close to that pre-set threshold, is performed.

[0031] Figure 6 shows another embodiment of implementation of the present method, wherein the inclined separation multi-sectional chamber is shown. It consists of the three sequentially installed sections 43' - 45', which are located along the conveyor 42 and the three sequentially installed sections 43" - 43"", which are placed across the conveyor, whereas, lower ends of all the sections are placed at equal height with respect to the conveyor 42. Such disposition of the sections inside the separation chamber allows to simultaneously ensure uniformity of fluidized bed layer, both in longitudinal and in cross section of the vertical chamber. Figure 7 shows distribution of particles of mineral raw-material being separated, inside the sections 43" - 43"", which are located cross the conveyor 42.

[0032] For practical implementation of the present method, a prototype installation was manufactured for separating wastes of ferrochrome production, aimed at further obtainment of ferrochrome. A process of pneumatic separating was carried out in the inclined separation chamber consisting of the three sequential sections (Fig. 4), and the angle of inclination to the conveyor plane was 55°. Prior to the beginning of pneumatic processing, wastes were preliminary ground to coarseness 0 - 6 mm and were supplied to the belt-type conveyor, with a conveyor belt made of grid with the mesh of 1 mm, width of 600 mm, motion speed of 0.5-1.5 m/s. The inclined separation chamber was performed with rectangular cross section of 600x150 mm and height of 900 mm and was separated inside by partitions into the three sections of equal cross section. The chamber was connected by air-ducts with the gravitational deposition chambers with diameter of 1200 mm and height of 2500 mm. Air flow in the separation chamber was selected in such a manner that a product is yielded in the chamber, said product not containing ferrochrome beads and having gravity less than 2.9-3.5 t/m³, and after passing through the chamber metallic ferrochrome with insignificant inclusions of slag, being a sellable concentrate, remained on the conveyor. The specified embodiment of the separation chamber allowed to uniformly distribute the fluidized bed layer and to increase 2.2 times the performance of the device in comparison to a single rectangular vertical separation chamber with section of 600x150 mm and height of 900 mm.

Claims

1. A pneumatic method of separating mineral raw materials, which comprises placing raw materials which are to be separated on an air-permeable surface which traverses a separation chamber with a rising air flow that lifts light fractions from the air-permeable surface, the latter being in the form of a conveyor passing beneath the lower base of the separation chamber, in which, by selection of the velocity of the air flow, a dilute fluidized bed layer is formed from particles of a specified density, into which less dense particles enter and through which said particles pass without obstruction before being transferred with the rising air flow out of the separation chamber into a gravitational deposition chamber, characterized in that the separation chamber is installed inclined towards the conveyor plane, whereas its lower base is parallel towards the conveyor plane and the acute angle formed by longitudinal walls of the separation chamber and its base is directed towards the conveyor motion.

2. The method according to claim 1, characterized in that the separation chamber is divided by internal longitudinal parallel partitions into two or more sequentially and/or in parallel positioned sections, whereas, lower ends of the sections are positioned in parallel to the conveyor plane, and upper ends of the sections are joined together inside the vertical separation chamber by the single air flow which transfers particles to the gravitational deposition chamber.

3. The method according to claim 2, characterized in that the sections of the separation chamber have cross sections which are equal by area.

4. The method according to claim 2, characterized in that the sections of the separation chamber have cross sections which are different by area.

5. The method according to claim 2, characterized in that lower ends of the sections of the separation chamber are placed at the same height with respect to the conveyor surface.

6. The method according to claim 2, characterized in that lower ends of the sections of the vertical chamber are placed at different height with respect to the conveyor surface.

Drawing